The present invention relates to CDMA mobile station apparatuses and CDMA transmission methods such as digital car telephones and portable telephones used for cellular radio communication systems.
For radio communication systems such as digital car telephones and portable telephones, a multiple access system is used in which multiple mobile station apparatuses perform communications with a single base station apparatus simultaneously. Recently, as one of these line switching systems using this multiple access system, a CDMA (Code Division Multiple Access) system is used because of its high frequency utilization efficiency.
Data transmission timing in a conventional CDMA mobile station apparatus is explained using a timing chart shown in FIG. 1.
FIG. 1A is a timing chart showing data transmission timing during data transmission. Pilot symbols (hereafter referred to as xe2x80x9cPLxe2x80x9d) and transmission power control symbols (hereafter referred to as xe2x80x9cTPCxe2x80x9d) are periodically inserted into data, forming a frame. When a portion from the start of a PL to the start of the next PL is calculated as one slot, one frame generally consists of 16 slots, 10 ms.
FIG. 1B is a timing chart showing data transmission timing during transmission on transmission standby. xe2x80x9cDuring transmission on transmission standbyxe2x80x9d means a time corresponding to less than K frames after completion of data transmission or a time corresponding to less than L frames in which a CRC detection of received data resulted in NG (K and L are predetermined constants). On transmission standby, the CDMA mobile station apparatus transmits burst data in which only a PL and TPC are written and other bits are left in blank for each slot.
Here, the CRC (Cyclic Redundancy Check) detection means processing for detecting errors in received data by judgment by a comparison between a received CRC bit which is given with a coefficient of a remainder polynomial obtained by dividing an information bit by an n-th degree generating function, and a CRC bit generated from the received data. A complete match between the two means that the received data have been received correctly (OK) and mismatch of at least one element means that the received data contain errors (NG).
FIG. 1C is a timing chart showing the data transmission timing at the end of transmission. The end of transmission means a state in which at least K frames are detected after data transmission is completed and at least L frames in which a CRC detection of the received data resulted in NG are detected.
As shown in FIG. 1C, the conventional CDMA mobile station apparatus stops transmission of burst data in a certain time after the end of communication in order to reduce power consumption of batteries by a transmission amplifier.
Because of this, the conventional CDMA mobile station apparatus above takes time to establish synchronization when restarting communication, and it has to send a dummy signal, an unnecessary signal, instead of data in the meantime until synchronization is established, resulting in a problem of reducing the transmission efficiency.
A first objective of the present invention is to provide a CDMA mobile station apparatus and CDMA transmission method which can maintain established synchronization with a base station apparatus while reducing power consumption when there are no data to be transmitted.
This objective is achieved by controlling the transmission interval of burst data to N slots (N: a natural number) when a certain time has elapsed after the end of data transmission.